The present application generally relates to an apparatus for setting a fastener by pulling on a stem of the fastener, and more specifically relates to a pulling head system for use with power tools for setting a wide range of fasteners.
Pulling heads are presently commercially available for setting fasteners. These pulling heads are configured for engagement with a power tool, such as a pneumatic or hydraulic power tool (these power tools are well known in the art; for example, the assignee of the present invention, Textron Inc., currently sells power tool model numbers G902, G746, G704 and G747 which can be used for such an application). Specifically, the pulling head is threadably engaged with the power tool, and jaws of the pulling head are engaged with the stein of a fastener when the fastener is positioned in an aperture in one or more workpieces. Then, the power tool is actuated, causing the pulling head to pull on the stem of the fastener, thereafter causing the fastener to set and the stem to break away.
Some pulling heads, such as that which is shown in FIG. 1, are regarded as being “straight” pulling heads, while others, such as that which is shown in FIG. 2 or 5, are regarded as being “offset”. As shown in FIG. 1, while straight pulling heads have one or more jaws 10 which are generally aligned with the pulling force (indicated with arrow 12) which is generated by the power tool (not specifically shown), offset pulling heads, such as that which is shown in FIG. 2 or 5, generally have one or more jaws 14 which are offset from the pulling force (indicated with arrow 16 in FIG. 2) which is generated by the power tool (not specifically shown). Offset pulling heads are typically used to set blind fasteners such as blind bolts, rivets, etc., which are located in hard to reach places. For example, with regard to airplanes, as aircraft structures get smaller and more complex, a large percentage of the fasteners are installed in hard to reach places, such as very close to other structures (i.e., small edge distance), in areas obstructed by other fasteners or aircraft structure, in blind areas (for example, inside of a C channel), or in tight areas obstructed on two, or even three sides. In all of these cases, a standard straight pulling head cannot be used, because it is too large to access such areas. For comparison purposes, FIG. 4 illustrates an offset pulling head 20 being used in an obstructed area 22, and a straight pulling head 24 being used in an open access area 26.
As mentioned above, FIG. 1 illustrates a straight pulling head. The pulling head 30 includes a sleeve 32 in which is disposed a collet 34. A nosepiece 36 threads into a threaded bore 38 which is provided at the end 40 of the sleeve 32. This is beneficial as the nosepiece 36 is therefore removable, and if it becomes worn it can be easily replaced. An opposite end 42 of the sleeve 32 is provided with two lugs for engagement into the head of a power tool (not shown), and a rear end 44 of the collet 34 is internally threaded for threading onto a piston of the power tool. Inside the collet 34 are disposed a set of three jaws 10 which are kept generally together by an o-ring 46. Rearward of the jaws 10 is a jaw follower 48, which consists of a sleeve 50 and a cap 52. A compression spring 54 is also provided, and the spring 54 works to spring bias the cap 52 away from the sleeve 50. As shown in FIG. 1, an angled, rear surface 56 of the nosepiece 36 engages an angled, leading edge surface 58 of each of the three jaws 10, thereby tending to spread the jaws 10 open. As shown, the collet 34 includes an undercut 60 on its interior surface 62 for accommodating expansion of the jaws 10. Furthermore, each of the jaws 10 includes a back, angled surface 64 which engages a corresponding conical surface 66 on the cap 52 of the jaw follower 48, also tending to spread the jaws 10 open. As such, the jaws 10 are normally open when no fastener stem is inserted into the nosepiece 36. This helps to limit wear on serrations 70 of the jaws 10 because the stem need not be slid through a set of closed jaws when the stem is initially inserted into the nosepiece 36.
Although the pulling head design shown in FIG. 1 has several beneficial features, such as the removable nosepiece 36, some disadvantages include the fact that the pulling head 30 can only be used to install a single type (i.e., size) fastener. Specifically, serrations 70 of the jaws 10 are designed such that the jaws 10 can only grip one size fastener, and the opening 72 in the nosepiece 36 is sized such that the pulling head 30 is limited with regard to how big of a stem can be inserted into the pulling head 30. Furthermore, the fact that the entire surface 64 on the back of jaws 10 is angled provides a relatively substantial undercut, and requires that the surface 64 must be machined, rather than cast. As such, the jaws 10 are relatively expensive to manufacture, difficult to inspect, and prone misalignment, leading to improper installation of fasteners. Also, due to the collet 34 having an undercut 60 for accommodating expansion of the jaws 10, the collet 34 is also relatively expensive to manufacture. The pulling head 30 is configured to be connected to a power tool having a certain stroke length to install a specific fastener. The pulling head 30 can be used with only one tool.
FIGS. 2 and 3 illustrate a prior art single jaw offset pulling head 100. Specifically, FIG. 2 provides a cross-sectional view, while FIG. 3 provides an exploded perspective view. As shown, the device provides a single jaw 14 which is biased by a spring 102 inside a drawbolt saddle 104. The jaw 14 has an angled surface 106 which engages a corresponding angled surface 108 on a drawbolt 110. The drawbolt 110 is disposed generally in a frame 112 of the pulling head 100, and a drawbolt adapter 114 is threadably engaged with the drawbolt 110. While one end 116 of the drawbolt adapter 114 is threadably engaged with the drawbolt 110, an opposite end 118 threadably engages a piston of a power tool (not shown). Likewise, one end 120 of a frame adapter 122 threadably engages the frame 112 of the pulling head 100, while an opposite end 124 of the frame adapter 122 threadably engages a head of the power tool (not shown). In addition, the pulling head 100 includes a dowel pin 126 for securing the drawbolt saddle 104 to the drawbolt 110, a roll pin 128 for facilitating sliding of the drawbolt 110 relative to the frame 112, a roll pin 129 for anchoring drawbolt saddle 104 to drawbolt 110, a guard 130 for enclosing an otherwise exposed portion of the tool 100, and a jam nut 132 for securing the pulling head 100 relative to the head of the power tool. The front end 139 of the frame 112 of the pulling head 100 has an opening 140 for receiving a stem of fastener that is desired to be installed, such that the stem can be gripped by the jaw 14 inside the pulling head 100.
In use, the pulling head 100 shown in FIGS. 2 and 3 is threadably engaged with an appropriate power tool (i.e., the end 118 of the drawbolt adapter 114 is threaded onto the piston of the power tool, the end 124 of the frame adapter 122 is threaded into the head of the power tool, and the jam nut 132 is secured down). Then, a stem of a fastener that is desired to be set is inserted into the opening 140 which is provided in the front end 139 of the frame 112. While the jaw 14 is spring biased closed by the spring 102, when the stein is inserted into the opening 140, the stem pushes the jaw 14 open and the jaw 14 springs back against the stem and becomes seated against the stein. Then, the power tool is actuated causing the piston to be pulled back, thereby pulling on the drawbolt adapter 114. Pulling on the drawbolt adapter 114 causes the drawbolt 110 and drawbolt saddle 104 to move back in the frame 112 (i.e., in a direction away from the opening 140 in the 15 front end 139 of the frame 112). Due to the fact that the jaw 14 has an angled surface 106 which engages a corresponding angled surface 108 on the drawbolt 110, movement of the drawbolt 110 in a direction away from the opening 140 in the front end 139 of the frame 112 causes the jaw 14 to grip and effectively lock on the stein of the fastener, whereby further actuation of the power tool eventually causes the stein to be pulled sufficiently such that the fastener sets and the stein breaks off.
While this system is very popular and addresses many of the limited access issues, it has some fundamental flaws. For example, the opening 140 in the frame 112, the jaw 14, and the overall stroke of the pulling head 100 shown in FIGS. 2 and 3 are all designed such that the pulling head 100 can install only one certain type of fastener. Additionally, the pulling head is expensive to maintain, and is not very reliable due to stein slippage caused by misalignment of the jaw 14. Finally, the offset pulling head 100 shown in FIGS. 2 and 3 has a relatively short tool life compared to a straight pulling head 30 such as is shown in FIG. 1.
FIG. 5 illustrates another prior art offset pulling head 200 which is commercially available. The pulling head 200 is much the same as that which is shown in FIGS. 2 and 3, except that the pulling head 200 shown in FIG. 5 has a different jaw arrangement. Specifically, while the pulling head 100 shown in FIGS. 2 and 3 includes a single jaw 14, the pulling head 200 shown in FIG. 5 has two jaws 202. The jaws 202 are retained in a collet housing 204, and a rubber sleeve 206 is glued onto the end 208 of the jaws 202. The rubber sleeve 206 tends to keep the jaws 202 relatively centered. The jaws 202 are kept closed when a stein is not inserted into an opening 210 provided in the front end 212 of the pulling head 200. An undercut 214 is provided inside the collet housing 204 to accommodate opening of the jaws 202 when a stern is inserted in the pulling head 200, and a cap 216 is threadably engaged with the collet housing 204. The cap 216 functions to compress the rubber sleeve 206 and hold the jaws 202 in place. If the cap 216 is adjusted properly, the cap 216 works to push on the rubber sleeve 206, thereby reducing its internal diameter 220 and slowing down spent stems (i.e., when a stem breaks off in the pulling head 200, the rubber sleeve 206 slows down the stem as the stem ejects back).
Disadvantages of the pulling head 200 shown in FIG. 5 include, but are not limited to the following: because the jaws 202 are kept closed and are forced open upon a stem being inserted in the opening 210 in the front 212 of the pulling head 200, there is increased wear on the jaws 202; and the undercut 214 which is provided inside the collet housing 204 to accommodate opening of the jaws 202 when a stem is inserted in the pulling head 200 makes the collet housing 214 expensive to manufacture and hard to inspect, and also reduces the overall strength of the collet housing 204, due to stress concentration. Furthermore, the capabilities of the pulling head 200 are limited to installing only the type of fastener for which the pulling head 200 is designed. The pulling head 200 is designed such that it can be used with one specific type of fastener. The pulling head 200 also has a relatively short stroke matching the intended fastener to be installed, and concentricity of the jaws 202 is controlled by the rubber sleeve 206 which is molded onto or glued onto the jaws 202, and this is unreliable. Finally, the pulling head 200 shown in FIG. 5 is expensive to manufacture and has an unreliable stem-retaining system, due to the pulling head 200 requiring accurate tightening of the rubber sleeve 206 (more specifically, the cap 216) in order to retain the spent stem—i.e., the rubber sleeve 206 works to slow down spent stems only if the cap 216 is adjusted properly. As such, failure to properly adjust pressure on the rubber sleeve 206, viz-a-viz the cap 216, can result in spent steins being ejected out of the pulling head 200 at high speed, which is a grave potential hazard.